Modern productivity requires automation of assembly whenever possible. In some devices, automation is essential for reproducible results. Modem thermometry or other quantifiable properties requires reproducibility for consistent standards.
Over the last 20 years, clinical thermometry has developed single-use, handheld thermometers that use precise quantities of different compositions of solid solutions of two thermally responsive materials in a plurality of cavities on a single strip of laminated material, each composition in each cavity alterable at a different temperature. The precision of the different compositions responsive to the different temperatures has permitted these chemical thermometers to be truly qualified as clinical devices.
A number of patents describe the advances made to this field of clinical thermometry. Among these patents are those issued to Hof et al. such as U.S. Pat. Nos. 4,232,552; 4,299,727; 4,345,470; and 4,397,570, which describe improvements to the temperature indicating compositions of matter, the all-plastic construction of the thermometer, and the like.
Automated assembly of the clinical thermometer reduces costs, improves productivity, improves quality assurance, and provides other benefits. In the assembly of a clinical thermometer where as many as 45 different compositions are being deposited in 45 separate cavities on the thermometer surface, precise metering and delivery of the compositions to the cavities, in registration, is essential for productive assembly of the clinical thermometers. U.S. Pat. No. 3,810,779 (Pickett et al.) discloses a method and apparatus for depositing precisely metered quantities of liquid on a surface, particularly temperature indicating compositions of matter on to the surface of a clinical thermometer. The method and apparatus disclosed in Pickett et al. has formed a basis for the construction of automated machinery to meter and deliver 45 different compositions to the 45 cavities for detecting temperatures ranging from 96.0.degree. F. to 104.8.degree. F. (35.5.degree. C. to 40.4.degree. C.). The Pickett et al. apparatus relies on a gravity feed of a composition that is a liquid at the temperature at which it is metered and delivered, yet a solid at ambient temperature.
Clinical thermometry has enjoyed the advances disclosed by the Hof et al. patents and the Pickett et al. patent because the thermometers can be precisely manufactured inexpensively and because the inexpensive clinical thermometers can be disposed of after a single use. The clinical thermometer can be taken, then the instrument disposed to avoid the transmission of viruses, bacteria, and other germs that unfortunately plague reusable thermometer devices.
Clinical thermometry also is benefitting from advances in the nature of the temperature indicating compositions of matter whereby the amount of energy and time needed to reverse the "firing" of one of the compositions in one of the cavities from freezing temperatures overnight to room temperatures for a few hours. Some of these new reversible thermometer compositions employ an emulsion of a thermally responsive material, means for observing a change in state of the material such as a dye, and a matrix forming material in which the thermally responsive material is dispersed. Reversible thermometer compositions of this type are disclosed in European Patent Publication 0 684 463 (A1) (Hof). The viscosity of the emulsion is considerably greater than the viscosity of the mixtures disclosed in the Hof et al. patents. Thus, the apparatus disclosed in the Pickett et al. patent that relies on liquid delivery of the compositions to the cavities is inadequate for automated assembly of the reversible clinical thermometers.